Conventional vehicle transmissions include software or a control scheme for determining when the automatic transmission shifts from one gear range (or ratio) to another gear range. This control scheme is commonly referred to as a “shift schedule” and is based on multiple factors, e.g., engine torque, vehicle speed, accelerator pedal position (i.e., throttle percentage), transmission output speed, and tractive effort. Any given shift schedule for a vehicle balances fuel economy against performance, and so a shift schedule may be categorized as an “economy shift schedule” or a “performance shift schedule” based on the balance that characterizes the shift schedule. For example, in an economy-biased shift schedule, a transmission operates in an economy shift schedule more often than it operates in a performance shift schedule.
Also, it is desirable to be able to change shift schedules during vehicle operation since there are times when better fuel economy is preferred over high-performance and vice-versa. For example, when the vehicle is heavily loaded or is ascending a steep grade, the transmission may detect such a condition and select a performance-based shift schedule. Alternatively, when the vehicle is able to quickly accelerate, e.g., when the vehicle is unloaded or descending a steep grade, the transmission may detect this condition and select an economy-based shift schedule.
In a conventional vehicle having an engine and automatic transmission, an engine control module (ECM) controls the engine and a transmission control module (TCM) controls the transmission. A wiring harness is provided that electrically connects the ECM to the TCM so that information related to the engine can be communicated to the TCM. Transmission software is downloaded to the TCM and includes multiple shift schedules that control when the transmission shifts from one gear ratio to another gear ratio. During vehicle operation, the TCM detects a driving condition or a change in a driving condition and selects a shift schedule accordingly.
For the transmission to detect the driving condition or the change in a driving condition, the TCM receives engine data from the ECM and possibly other information about the vehicle from other sources. As such, the transmission must be compatible with the engine and other outside sources to receive this information. For a transmission to operate effectively with the engine, transmission manufacturers must work closely with engine manufacturers to ensure that the TCM timely receives engine data from the ECM. As a result, transmissions can only be mounted behind engines from which the TCM is able to receive engine data.
If a transmission were mounted behind an engine with which it is not compatible, the ECM might not be able to communicate engine data (e.g., engine torque) to the TCM and the TCM might therefore be unable to select the appropriate shift schedule. Alternatively, even if the ECM were able to communicate engine data to the TCM, the ECM still might not be able to communicate the correct data or might provide the data to the TCM too slowly. As a result, as driving conditions change, the TCM would be unable to select a different shift schedule based on the changing driving condition because it would be waiting to receive engine data from the ECM. These problems undesirably limit the number of vehicles in which a given transmission can be installed and require costly and time-consuming coordination efforts between engine and transmission design teams.
In addition, some transmissions can only operate in an economy mode or performance mode based on the type of shift schedule being performed. As such, a transmission can be shifting between gear ranges according to shift points in a performance shift schedule and be unable to switch to an economy shift schedule under certain conditions. Alternatively, a transmission may be able to switch between shift schedules, but the vehicle productivity is negatively affected.
What is needed is an improved system of selecting a transmission economy-based shift schedule when fuel economy can be improved and vehicle performance will not be negatively affected. Further, it would be desirable to be able to select the economy-based shift schedule quickly and without regards to the shift schedule under which the transmission is performing at the time of making the selection.